The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1887-11-22
From the Wood Fire to the FresneI
System.
Fixed, Revolving, Flash and coIored
Lights.
fBy NJ. A. Hanna.l

~ lit the lamps In the lighthouse tower,
The sun dropped down and the day was dead;
They shone like brilliant clustered flower
Ten golden and FIVE red"
That was in the days Of the old reflector.
(catoptric) system Of fifty or sixty years ago.
and the kind or character Of light must have
been what was then designated as revolving,
red and white. At that period the only dis
tinguishing characteristics used were fixed
white, fixed red. revolving. either red or
white, and two lights. In primitive light
houses no attempt was made to introduce
any features by which are light could be
distinguished from another, nor was 1t nee
essary since there was in no case more than
one light at the entrance OF any Important
port Indeed, some nations OF considerable
commercial prominence, had but a single
beacon, and that was located at the entrance
Of the principal port.
Fires Of wood burned In a stone lantern
or CRATE, at the top Of the tower, was the
earliest method Of Illumination.
Fires we're also sometimes kept burning on
the SUBMITS Of high hills near sea-ports for
the purpose Of guiding the ancient mari
ner." A fire Of this nature, was, believe
guide an expected snip to port.
The first real lighthouse built on this con-
tinent was erected on Little Brewster Isl
and, main entrance to Boston harD0r. ltlS
said to have been built solid Instead OF eylln-
drical, and that the summit was gained Dy
means of ladder. 1t Is known, however,
that prior 10 building the lighthouse, a sort
Of irregular beacon, had, for some time, been
maintained on Point Allerton, prominent
headland near the entrance OF the harbor. =.
Pitch and Oakum, In the form OF Dales
or balls" burned in an iron Drazler or
basket, was the principal method OF illumi-
nation, though wood was also used.
1t was sometime In the eighth decade OF
the last century that rehectors began 70 be
used in lighthouses, and IL Is recOrueu tnas
though some lights had nearly a hundred
lamps, each with a reflector, the light was 50
poor that mariners prayed for return 20
the preceding method OF coal and wood nres.
The parabolic reflector, invented by M.
Borda, as were also revolving lights, wasa
gigantic stride toward perfection In light
house Illumination Strange to say, the ap--
plication Of this invention, as well as that OF
the lenticular system, by M. Fresnei, was
greatly delayed for 1.-THE lack OF
artisans expert ds. enSusa Io} The y invenEor
All lights are now provided with the Fesnei
lens apparatus, from which they each and
all derive their chief power and Drilhancy.
The lenses are all made OF natural color
glass, no cOlOrlng udbtcI WhatoNOA wins
used In their composition.
These lenses range in size from FIRST order
one IL feet high by 6 feet inches in diam
eter, down to the various grades 10 one Of
the sixth order, about Is inches high by 10
inches diameter. A light Of the first order
has five wicks concentrically arranged, the
outer one being over five inches IN diameter.
A light Of the second order has three w1ckst
light of the third order has two, and ali
lesser orders have one each. Very few peo.
h.arl anu I'm nN4y All
the methods by which the many character
lists, some 20 in all, are produced Dy
the lenticular system. -
AN lenses of the larger orders are Of the
same diameter from the base ring up 10
about two-thirds their height, and are tnen
crowned by cup0a OF prismatle rings so
arranged as to bend the rays OF nght 70 tne
horizon. A first order lens has Is OF these
rings in its dome-like top.
There are also eight OF these rings In tne
sections described is the lenticular drum
the principal as well as the more powerful
part of the apparatus.
For a fixed light this drum is cylindrical In
design, and forms perfect plano-conyex
circle around the lamp, and In nrst order
lerfs is feet inches in diameter by feet
elevation.
By making fame Of sufficient volume ir
the exact centre Of the described dTlm.
fixed white light Is the result. by. sp0stitut-
. II
ural glass, we obtain fixed red light. To
produce a revolving or flashing light, the
lens drum is made p0yg0nal IN shape IN
stead Of circular, and 1t may have from SIX
TO "A sides, according as the time between
flashes Is to be longer or shorter. BY r0tat-
ing this apparatus around the lamp we OBJ
tain flashing light and 1t Will be red or
white according TO the color Of the chimney
used.
For fixed light varied by flashes, the lens
fs far ,oA aoraofo1Iu tho
and is composed Of alternate plano-convex
and annular (bulls-eye) sections. BY caus-
ing this TO revolve around the lamp we get
a light of the character named, and the kind
Of chimney used will make II either red or
white. The western light at the Cape Eliza
beth station is light Of this character, and
it shows flash of four seconds, partial
eclipse Of six seconds, followed by hxed light
of so seconds, every 90 seconds. NO color
Is used, and u IS therefore wnlts.
Of the light Is to be fixed white, varied by
red flashes. This result Is obtained by plac-
ing panels Of red plate glass in front Of each
of the annular OF "bulP s-eye sections OF
lens like the last one described. Inc req
panels revolve with the lens, and red Hash
is exhibited to the observer every time
colored panel passes between him and the
flame. The spaces between the red panels
will show fixed white light. Ot course the
reader understands that plain glass cnlm.
would be fixed red, varied by red flashes, and
the red panels would be superfuOus. III a
lens be formed with all annular or bull s-eye
sections (polygonaD and panels OF red glass
be fixed 20 and in front OF every other sec
tion. by revolving it around flame covered
with plain chimney we get an alternate red
and white flashing light.
IL the red, vertical panels cover only every
third section Of the lens, we get still another
distinction, two white flashes, succeeded by
red one.
In all revolving OF flashing lights there is
partial eclipse between the flashes, which be-
comes total If the observer Is distant, say
half the lights Erangeaof Visibility ana tar-
ther.
The sew, raj degrees of size and intensity,
and the many degrees Of length Of flash and
interval, varying from a few seconds 10
three minutes, together with Otner cOmDinA-
tiOns, of which / have only given some OF
the simpler ones, is what makes the Fresnel
system superior TO any other method Of light
house illumination.
Another distinctive feature, introduced
within a few years, Is the white light with
red sector. This Is for harbor or inland
lights only. and the object is TO cover either
dangerous shoals or the channel approaches
by beam of cOlOred light A narrow strip
OF red glass is fixed in the lantern (not lens)
of lust sufficient width so that the divergent
red rays will illumine the safe course or
track Of vessels bound for OF from the har-
Dor.
The Ram Island light, near the entrance
to BoOthbay, is beacon Of this description:
1t Is a fixed white light, with two liked red
rays, one covering the eastern, the other the
western approach, from seaward, to Booth
bay harbOr.
Lighthouse Illumination, from the time Of
the Pharos Of Egypt, with wood fire at its
summit, b. g. 800, down to Liberty En-
tightening the World" with her torch OF
electric light, forms one Of the most interest
ing chapters in the whole range Of physics.
News from North Haven.
Capt. James l.. Crockett Of the +. II.
Smith intends spending the winter in